Just recenty, when in D4 drive, let up off accelerator and coast to slower , we would hear a slight grinding( more like a fast chattering noise), that would go away when accelerating. The noise would come to a stop as you would near slow down. D3 is fine.

Now reverse stopped working. I can tell that engine idle goes DOWN in Park, It goes Up when shifting into reverse. As if there is some sort of mode control problem

In spite of all this, the automatic transmission shifts fine in D3 or D4

No proof yet, but I think transmission computer issue, or shift solenoid

Any thoughts?

Many thanks